For simplicity bus diagrams show parallel lines in place of the twisted pairs of wires used in practice. A: You can. The RS standard specifies a maximum of ten ohm unit loads for bus receivers.
A: An RS network allows as many as 32 drivers and 32 receivers. Some equipment and interface cards include an RS driver and a receiver, while others might provide only a driver or only a receiver. We use the term duplex to describe this type of back-and-forth communication.
When your system requires a response from some devices or when more than one driver must communicate with various receivers, choose RS products. The RS standard allows half-duplex and full-duplex communications. A half duplex arrangement connects all receivers and drivers to the same 2-wire bus as shown in Figure 2. In a full-duplex network, a driver can communicate with one or more devices and then another driver can use the bus to report results or send commands to other receivers.
Figure 3 shows a portion of a full-duplex network that requires four wires for differential signaling. Figure 2. A half-duplex RS network uses two conductors for communications between a controller and equipment. When commanded to reply with data, a slave device connects its driver to the bus and transmits bits to the controller at the left. In this network, the Indicator device has no need to reply.
Figure 3. This full-duplex RS arrangement provides for simultaneous 2-way communications. The slaves respond — one at a time — via the bottom bus. A: Differential refers to a voltage difference created by a driver on the two signal lines.
Both RS and RS use a twisted-pair wire i. The main difference between RS and RS is that while RS is strictly for point-to-point communications and the driver is always enabled , RS can be used for multidrop systems and the driver has a tri-state capability.
The electrical characteristics of the balanced voltage digital interface are designed to allow use of both balanced and unbalanced see EIA Standard RSA circuits within the same interconnection cable sheath. For example, the balanced circuits may be used for data and timing while the unbalanced circuits may be used for low speed control functions.
Since the basic differential receivers of RSA and RSA are electrically identical, it is possible to interconnect an equipment using RSA receivers and generators on one side of the interface with an equipment using RSA generators and receivers on the other side of the interface, if the leads of the receivers and generators are properly configured to accommodate such an arrangement and the cable is not terminated. The balanced interface circuit is not intended for interoperation with other interface electrical characteristics such as RSC.
Under certain conditions. Making sense of cable specifications Selecting data cable for an RS or RS system isn't difficult, but often gets lost in the shuffle of larger system issues. Care should be taken. Beyond the obvious traits such as number of conductors and wire gauge, cable specifications include a handful of less intuitive terms.
Characteristic Impedance Ohms : A value based on the inherent conductance, resistance, capacitance and inductance of a cable that represents the impedance of an infinitely long cable. When the cable is out to any length and terminated with this Characteristic Impedance, measurements of the cable will be identical to values obtained from the infinite length cable. That is to say that the termination of the cable with this impedance gives the cable the appearance of being infinite length, allowing no reflections of the transmitted signal.
If termination is required in a system, the termination impedance value should match the Characteristic Impedance of the cable. Systems with long lengths benefits from using low capacitance cable. That page also re-affirms that the hysteresis is 50 mVp-p. As for the cable - it has a characteristic impedance and if not reasonably properly matched by loading resistors there can be reflections that cause errors. It doesn't matter what serial comms method you employ or what the nominal cable impedance is.
Take a look at thispicture for a 50 ohm system: -. So, you terminate the cable to minimize the possibility that reflections can break thru the hysteresis level of the receiver and create a data output error. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. RS charachteristic impedance and its variants Ask Question. Asked 6 years, 2 months ago.
Active 6 years, 2 months ago. Viewed 4k times. Will this work out? Board-Man Board-Man 1, 22 22 silver badges 57 57 bronze badges. Also, the characteristic impedance of a cable remains unchanged whatever load you apply. The supply rails are 3. So what you say is that with the circuit I showed in my question, the impedance of the line remains R standard RS despite adding the 53R and R. If so, then why do we have termination resistors in differential lines if there is no impact on the charachteristic impedance?
Now, suppose the driver is interfaced. I must be looking at the Difference in differential output VT - VT rating to be inside the rated voltage input differential of the receiver, right?
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